Polysilicon has hitherto been used in electrodes or conductors of LSI semiconductor devices. The tendency toward higher integration of LSI semiconductor devices has caused to present the problem of delay in signal transmission due to its resistance. Meanwhile, there is a demand for higher-melting materials to be used as electrodes to facilitate the formation of conductors etc. by self-alignment technique. Under these circumstances, conductors and electrodes of metal silicides that possess lower electric resistivity than polysilicon and are compatible with the silicon gate process have come into use. Examples of the metal silicides are tungsten silicide (WSi.sub.x), molybdenum silicides (MoSi.sub.x), tantalum silicides (TaSi.sub.x), titanium silicides (TiSi.sub.x), cobalt silicides (CoSi.sub.x), chromium silicides (CrSi.sub.x), nickel silicides (NiSi.sub.x), and silicides of platinum group metals.
A film of such a metal silicide is formed by sputtering a target of the metal silicide. The silicide target used often has a silicon/metal molar ratio greatly in excess of 2, because when a molar ratio x is less than 2, stresses in the film becomes higher as the film is formed and the film tends to peel away from a substrate.
Metal silicide targets are manufactured by mixing silicon powder and a specific metal powder in a silicon/metal molar ratio of 2 or more, synthesizing the mixture to a synthesized silicide powder, compressing and sintering the synthesized silicide powder, and then machining the sintered body to a desired shape.
The recent rise in the extent of integration of LSI semiconductor devices (e.g., to 4, 16, and 64-megabits) has reduced the width of their conductor lines finely to submicron levels. With this tendency the particles generated from the target are attracting attention as a subject of growing concern. The term "particles" as used herein means the particulate matters scattered and flew around from a target on sputtering of the target. The particles deposit directly on the film on a substrate or stick and build up on surrounding walls and parts and then come off to deposit on the film, inviting severe troubles such as breaking and shorting of conductor lines. The particle problem is becoming more and more serious with the progress of integration and refinement of the circuit of electronic devices. Thus it is noted anew that the conventional silicide targets are unsuitable for the VLSI applications because they generate too many particles during sputtering.
It has already been recognized in the art that coarse ones of free silicon phases contribute largely to the generation of particles from metal silicide targets. On the basis of this recognition, e.g., Japanese Patent Application Public Disclosure No. 191366/1992 discloses a metal silicide target of a refractory metal and Si characterized in that the average diameter of free Si particles is 30 .mu.m or less and the number of free Si particles having diameters of 40 .mu.m or more present in the surface and cross section of the target is 50 or less per square millimeter, and also a method of manufacturing the target. Patent Application Public Disclosure No. 1370/1993 previously filed by the present applicant imposes a stronger requirement, disclosing a metal silicide target characterized in that the number of coarse silicon phases 10 .mu.m or larger in size that appears in the sputter surface of the target is 10 or fewer per square millimeter, and also a method of manufacturing the same.
Patent Application Public Disclosure No. 257158/1991, which is directed to a refractory metal alloy target rather than a silicide target to which the present invention relates, teaches that the surface roughness of the target is desirably 0.05 .mu.m or less, on the basis of the discovery that the generation of particles is ascribable to the surface defect layer, surface conditions, residual stresses that result from the machining of the sintered body of target.
Our further practice has led to the new finding that the mere restriction of the number of coarse silicon phases 10 .mu.m or larger that appear on the sputter surface of a metal silicide target is not satisfactory in that the number of particles generated is still considerable. In the case of the aforementioned Patent Application Public Disclosure No. 257158/1991, the surface roughness of the refractory metal alloy target is reduced to 0.05 .mu.m or less with the view to removing the surface defective layer and residual stresses so as to eliminate the particles caused by them. The same surface treatment is considerable also to the metal silicide target, but surface conditioning down to 0.05 .mu.m or less requires a very long time period in the case of the metal silicide target. With tungsten silicide, e.g., polishing the surface down to 0.04 .mu.m by electropolishing that is the most ordinary surface treating means takes as long as 100 minutes. This means that the treatment is practically of no use. In the case of metal silicides the silicon phases take part in the generation of particles, so that the particles number is extremely numerous and is in the range from 7000 to 8000 per piece of wafer. Thus there is an urgent need for substantially decreasing the number of particles by technical means capable of easily being put to practical use.